This invention relates to an automatically controlled clutch between an engine and a drive train of a motor vehicle, having a monitoring device which records rotational speed differences between the clutch input and the clutch output.
Motor vehicles with manually shifted transmissions and an automatically controlled clutch are basically known.
When controlling the automatic clutch and when monitoring the clutch, it is, in principle, desirable to detect rotational speed differences between the clutch input and the clutch output. This facilitates a no-jolt engaging and disengaging of the clutch and also permits detection of the thermal stress on the automatic clutch without measuring the temperature, since a computer simulation is carried out by which temperature conditions at the clutch are computed from the rotational speed difference, from the respectively transmitted clutch torque which is detected by corresponding sensors, and from the time history of the rotational difference and the clutch torque. The fact that the thermal dissipation losses occurring at the clutch are proportional to the product of the coupling torque and the rotational speed difference is utilized in this case.
It is an object of the invention to detect the rotational speed differences between the clutch input and the clutch output at low expenditures.
According to the invention, this object is achieved by determining the above-mentioned rotational speed differences from the signals of a first rotational speed measuring arrangement at the clutch input or non-rotatably connected on the vehicle engine as well as from the signals of another rotational speed generator arrangement on drive wheels of the vehicle, taking into account the respective ratio or position of a transmission between the clutch and the drive wheels, but while fading out rotational speed variations with a frequency which corresponds to a resonant frequency of the drive train when the clutch is closed.
The present invention is based on the general idea of using such rotational speed measuring arrangements which must exist in the vehicle anyhow for determining the rotational speed differences between the clutch input and the clutch output. The first rotational speed measuring arrangement is required in the case of modern motor vehicle combustion engines which are controlled with the goal of minimizing harmful exhaust gases. The second rotational speed measuring arrangement is always required for braking systems of a vehicle having an anti-lock system or control (ABS). The transmission ratios between the rotational speeds of the clutch output and the drive wheels are constructively defined. It may only be necessary to detect which transmission position or which gear is engaged. This is necessary or desirable anyhow for optimal control of the clutch torque when the clutch is engaged and disengaged.
Furthermore, the invention takes into account the recognition that, when the clutch is closed, characteristic bucking vibrations occur in the drive train, with the result that the ratio between the rotational speeds of the vehicle engine and the rotational speeds of the drive wheels of the vehicle fluctuates at a characteristic frequency of, for example, 4 to 5 Hz. The frequency of these bucking vibrations, which occur when the clutch is closed, is clearly lower than the frequency of grabbing vibrations occurring when the clutch is engaged or disengaged when the clutch is still slipping; that is, the clutch torque is still lower than the torque effective between vehicle engine and the drive train. Therefore, in comparison to the bucking vibrations, the grabbing vibrations have a clearly higher frequency which is increased approximately by a factor of 2 because, as a result of the not-yet closed clutch, the moments of inertia of the engine cannot be frequency-determining for the grabbing vibrations in the drive train.
In the present invention, the bucking vibrations are "faded out" during the analysis of the rotational speed differences between the engine and the drive train. It follows that an analogously fluctuating rotational speed difference between the clutch input and the clutch output from corresponding vibrations of the rotational speeds of the engine and the drive wheels, and therefore determination of an erroneous slipping clutch condition, is prevented.
As a result, the invention also makes it possible, in the case of extremely elastically flexible drive trains, to draw a conclusion from the signals for the rotational engine speed as well as the rotational wheel speed in a manner which is not falsified by bucking vibrations with respect to rotational speed differences between the clutch input and the clutch output.
As required, without being disturbed by bucking vibrations, the function of one of the sensors detecting the clutch torque can be examined in that it is sensed whether simultaneously disappearing rotational speed differences between the clutch input and the clutch output and a sufficiently large clutch moment exist in the case of which the clutch would have to operate without slip.
In addition, with respect to preferred characteristics of the invention, reference is made to the claims as well as to the following explanation of the drawing by means of which a particularly advantageous embodiment is described.